Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session D24: Microscale Flows: Devices |
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Chair: Kathleen Feigl, Michigan Technological University Room: Georgia World Congress Center B312 |
Sunday, November 18, 2018 2:30PM - 2:43PM |
D24.00001: Insect-inspired flow control in microfluidic networks Krishnashis Chatterjee, Philip Graybill, Joel Garrett, Rafael Davalos, Jake Socha, Anne Staples In earlier work, we incorporated key features of respiratory kinematics in some insect species, in the design of single-channel 3-layer, PDMS-based microfluidic devices and found that they produced unidirectional flows that reversed direction based on the frequency of actuation alone. In the present study, we use the same principles that serve to actuate the tracheal system to design and test four different insect-inspired microfluidic networks. In these devices, a pressure signal from a single source is distributed over the entire network and used to collapse the ceiling of the flow channel at multiple sites. We found that variation in the frequency of actuations can be used to regulate the magnitude of flow rates into different branches of the network. Additionally, we observed that in two networks, changes in actuation frequency drive the flow into a particular branch or completely shut it off, an unexpected finding. This novel feature- pumping selectively into certain branches in the network in a valveless device- has the potential to reduce the actuation overhead in microfluidic devices for applications including microscale chemical analysis, mixing, and cell sorting. |
Sunday, November 18, 2018 2:43PM - 2:56PM |
D24.00002: Transverse Migration and Concentration of DNA in Microfluidic Channels Jason E Butler, Ryan J Montes, Anthony JC Ladd The migration and subsequent concentration of long strands of DNA due to a pressure driven flow and parallel electric field within a microfluidic channel were measured. The concentration rate and efficiency of trapping the DNA were quantified as functions of the channel size and the ionic and polymeric concentrations of the buffer solution. Buffers with large ionic concentrations hinder the ability to concentrate the DNA at the entry of the microcapillary and reduce the short-time efficiency of the trapping from nearly 100% under optimum conditions to zero. The results also demonstrate that flexible strands of DNA migrate transverse to an applied shear flow and opposing electrophoretic flow, even when the buffer solution lacks any measurable viscoelastic response. Optimizing the electric field strength can increase the amount of DNA that can be trapped, and the efficiency is not affected by the size of the channel cross-section. The results are qualitatively consistent with a model for DNA migration that incorporates velocity disturbances induced by the electric field acting on the polyelectrolyte. |
Sunday, November 18, 2018 2:56PM - 3:09PM |
D24.00003: Velocity Gradient Focusing in a Free-Flow Electrophoresis Device for Protein Fractionation Matthew Courtney, Ethan Thompson, Tomasz Glawdel, Carolyn L. Ren Free-flow electrophoresis (FFE) devices enable the separation and collection of chemical species for applications in protein and DNA analysis. FFE operation is achieved by applying an electric field perpendicular to the flow of a liquid solution that is pressure-driven through a separation chamber. Analytes are injected at the beginning of the chamber, and then separate in the transverse direction based on their electrophoretic mobility. The fractions of analytes are then collected at different outlets. The present work highlights a novel FFE device that introduces a velocity gradient to counteract the electrophoretic migration, and therefore allows analytes to focus at unique positions in the chamber, where they experience a net force of zero in the transverse direction. This electrofocusing method, which serves to enhance resolution and sensitivity, is more versatile than traditional techniques, such as isoelectric focusing. The FFE device uses a simple fabrication approach for a microfluidic chamber that reduces Joule heating, and operates in the laminar flow regime. For validation, COMSOL simulations will be presented, followed by experimental results for the separation of different dyes and biomolecules.
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Sunday, November 18, 2018 3:09PM - 3:22PM |
D24.00004: Optimal design of deterministic lateral displacement device for cell sorting Gokberk Kabacauglu, George Biros We solve a design optimization problem for deterministic lateral displacement (DLD) device to efficiently sort same-size red blood cells by their deformability. Such optimal designs enable rapid medical diagnoses of several diseases such as malaria since infected cells are stiffer than their healthy counterparts. DLD device consists of pillar arrays in which pillar rows are tilted and hence are not orthogonal to the columns. This arrangement separates cells laterally depending on their deformability. Pillar cross section, tilt angle of the pillar rows and center-to-center distances between pillars define a unique device. For a given pair of cells with different deformability we seek optimal DLD designs. We fix all the parameters except the pillar cross section which we parameterize with uniform 5th order B-splines. We propose an objective function to capture efficient cell sorting. The objective function is evaluated by simulating the cell flows through a DLD using our 2D model based on a boundary integral method. We solve the optimization problem using a stochastic, derivative-free algorithm. We present several scenarios where the optimal designs can sort cells with slightly different deformability. These designs have cross sections that have features similar to a triangle. |
(Author Not Attending)
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D24.00005: Acoustic Stabilization and Enhanced de-Stabilization of Single Bubbles in Microfluidics and the Connection to the Acoustic Landau-Levich Coating Problem Amihai Horesh, Daniel Khaikin, Anna Zigelman, Ofer Manor The manipulation of liquid films over a vibrating solid substrate have been investigated for over thirty years. Applications for such systems include floatation unit operations, intense purification of water, drag delivery and cancer treatment and microfluidics. We recently showed that the excitation of SAWs in a microfluidic channel might destabilize the micron thick film of liquid between a bubble and a solid substrate at close proximity, rendering attachment. Our results correlated very well with a model for the Landau–Levich type coating of a solid substrate by a liquid film under the action of a propagating MHz frequency SAW. We were able to show that the conditions that rendered the acoustic Landau–Levich coating film unstable in theory further supported the enhanced destabilization of the micron thick liquid film, which resulted in the fast attachment of the bubble to the substrate. Here, we present new experimental results in which the conditions that render the acoustic Landau–Levich coating film stable in theory further supporting the stabilization of the micron liquid film between a bubble and a solid substrate. The film remains stable, resisting thinning, destabilization, and breakage, which will naturally occur in the absence of the SAW excitation. |
Sunday, November 18, 2018 3:35PM - 3:48PM |
D24.00006: Microfluidic tools for the screening crystallization conditions of monoclonal antibodies Sandy Morais, Gérald Clisson, Jacques Leng, Jean-Baptiste Salmon In the framework of the European research project AMECRYS, we developed microfluidic chips for studying protein crystallization processes. The challenge is to combine membrane-assisted crystallization and mesoporous silica 3D-nanotemplates to enable the crystallization of structurally complex proteins, such as anti-CD20 mAbs (monoclonal antibodies), one of the most important advances in the treatment of lymphocytic leukemia and autoimmune disorders. We developed original microfluidic devices making use of controlled pervaporation through thin PDMS membranes, to perform high-throughput screening experiments mimicking classical hanging drop experiments. Our devices make possible to control in time the concentration of solutes within multicomponent phase diagrams (protein/salt/crystallizing agent) and allow performing simultaneously analytical measurements. We determine the full phase diagram of crystallization experiments of anti-CD20 in a given aqueous two-phase system. We also show that the integration of miniaturized Quake valves makes also possible to investigate the possible role of recirculating flows on the growth rate of mAbs crystals. |
Sunday, November 18, 2018 3:48PM - 4:01PM |
D24.00007: A microfluidic suction pump using a super absorbent polymer Jaedeok Seo, Cong Wang, Jungyul Park, Wonjung Kim We propose a portable, non-powered suction pump driven by hydrogel for microfluidic devices. The development of portable microfluidic devices has often been limited by the need for external pumps. We have developed a microfluidic suction pump by enclosing a super absorbent polymer in a housing with an extended surface area for water absorption. The pump has a remarkably high flow rate of ~100 μl/min and an absorption volume of ~15 ml, thus far superior to the previously reported non-powered pumps. We constructed a portable energy harvesting system by combining the hydrogel pump with a reverse electrodialysis (RED) device. This portable system, powered by saltwater only, has successfully delivered enough power to operate small LEDs by generating an output density of ~ 100 μW / cm2 for an hour. Our hydrogel pump would make a breakthrough in developing portable microfluidic systems. |
Sunday, November 18, 2018 4:01PM - 4:14PM |
D24.00008: Optimal design of open capillary channel arrays to maximize evaporative mass flux Jungtaek Kim, Ho-Young Kim Plant leaves and heat pipes commonly involve microscale flow systems where liquids wicking into open channels undergo evaporation. Here we are interested in obtaining the optimal design of open capillary channel arrays to maximize evaporative mass flux. To increase the liquid evaporation, the liquid flux via wicking into the channel arrays should be enhanced. In addition, the evaporative mass transfer from liquid to surrounding gas should be facilitated, which is sensitive to the effects of contact line. That is, for hydrophilic channels, the evaporation flux is greatly enhanced near the solid-liquid-gas contact line. Thus, increasing the contact lines can be more effective than simply increasing the liquid-gas interfacial area. We experimentally measure and theoretically rationalize the evaporation flux from various widths of microscale open channels under the effects of contact line. We further consider the effects of overlapping diffusion boundary layers caused by too narrowly spaced channels. Then we provide a mathematical rule to optimize the channel width and spacings that can maximize the evaporative mass flux of liquid wicking into open capillaries. |
Sunday, November 18, 2018 4:14PM - 4:27PM |
D24.00009: Modeling microdistillation within microfluidics devices Benjamin Aymard, Marc Pradas, Serafim Kalliadasis Distillation is a well-known and widely-used process for the separation of binary fluids based on their differences in volatilities. The microscale counterpart, microdistillation, is a relatively new process, where surface tension becomes dominant over gravity, but has received little attention so far. Specifically, a temperature gradient is imposed across a microfluidic chip such that the temperature in the middle is above the boiling point of phase A and below that of phase B. A mixture introduced in the middle will undergo a phase separation, where one phase will evaporate while the other remains liquid. The distillate phase is then collected at the hot end of the chip, and the remaining phase at the cold output. Enhancement is achieved by guiding liquid phase using micropillars. From the modeling point of view this problem is challenging as it couples different physical processes of fluid mechanics and thermodynamics within a complex geometry. Here we present a diffuse-interface approach to model flow and phase change in confinement, by incorporating different levels of complexity progressively, ensuring that the system respects key equilibrium properties at each stage. |
Sunday, November 18, 2018 4:27PM - 4:40PM |
D24.00010: Comprehensive Modeling of Capillary Flow and Evaporation in Micropillar Wicks Geoffrey Vaartstra, Zhengmao Lu, Evelyn N Wang Porous wicks are commonly found in nature as organisms seek to leverage capillary forces for passive liquid transport. This natural mechanism has inspired great interest to incorporate wicks into engineered systems, particularly microscale devices. In this work, we modeled flow and thin film evaporation in micropillar wicks, which have been proposed for various heat transfer devices. These arrays of cylindrical pillars can generate large capillary pressures and have high permeability, enabling passive liquid supply via capillary-driven flow. The driving capillary pressure gradient entails variation of the liquid-vapor interface shape amongst micropillar cells that must be captured to accurately model physics on a millimeter scale wick. We overcame this challenge by conducting parametric studies of laminar flow and heat transfer for single micropillar cells over a range of geometries and interfacial curvatures. These parametric studies were integrated into a computationally efficient device level model that accounts for effects of local interfacial curvature on permeability and heat transfer. This modeling framework is capable of mapping pressure and temperature distributions on micropillar wicks, and can be broadly applied to porous wicks with periodic microstructures. |
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